class Hashie::Dash

API for defining properties as well as per-property defaults.
It is preferrable to a Struct because of the in-class
resources than something like a DataMapper resource.
lightweight data object that needs even fewer options and
Dashes are useful when you need to create a very simple
optional defaults) and only those keys may be set or read.
that has a set of defined keys that are accessible (with
A Dash is a ‘defined’ or ‘discrete’ Hash, that is, a Hash

def self.inherited(klass) 

def self.inherited(klass)
  super
  (@subclasses ||= Set.new) << klass
  klass.instance_variable_set('@properties', self.properties.dup)
  klass.instance_variable_set('@defaults', self.defaults.dup)
end

def self.property(property_name, options = {})


Dash.
to be returned before a value is set on the property in a new
* :default - Specify a default value for this property,

as follows:
Defines a property on the Dash. Options are 
def self.property(property_name, options = {})
  property_name = property_name.to_sym
  self.properties << property_name
  if options[:default] or self.defaults[property_name]
    self.defaults[property_name] = options[:default] 
  end
  unless instance_methods.map { |m| m.to_s }.include?("#{property_name}=")
    class_eval <<-ACCESSORS
      def #{property_name}
        _regular_reader(#{property_name.to_s.inspect})
      end
      def #{property_name}=(value)
        _regular_writer(#{property_name.to_s.inspect}, value)
      end
    ACCESSORS
  end
  if defined? @subclasses
    @subclasses.each { |klass| klass.property(property_name, options) }
  end
end

def self.property?(name)

defined.
Check to see if the specified property has already been 
def self.property?(name)
  properties.include? name.to_sym
end

def [](property)

property's default value if it hasn't been set).
Retrieve a value from the Dash (will return the 
def [](property)
  assert_property_exists! property
  super(property.to_s)
end

def []=(property, value)

on pre-existing properties.
Set a value on the Dash in a Hash-like way. Only works 
def []=(property, value)
  assert_property_exists! property
  super(property.to_s, value)
end

def assert_property_exists!(property) 

def assert_property_exists!(property)
  unless self.class.property?(property)
    raise NoMethodError, "The property '#{property}' is not defined for this Dash."
  end
end

def initialize(attributes = {}, &block)

just like you would many other kinds of data objects.
You may initialize a Dash with an attributes hash 
def initialize(attributes = {}, &block)
  super(&block)
  self.class.defaults.each_pair do |prop, value|
    self.send("#{prop}=", value)
  end
  attributes.each_pair do |att, value|
    self.send("#{att}=", value)
  end if attributes
end